The present invention relates to rotatable tool bodies of the type mounted in a machine for cutting hard surfaces and, in particular, an improved method of cold forging such tool bodies.
Machines for cutting hard surfaces, such as concrete and asphalt, provide for a rotating wheel or drum with a plurality of cutting tools mounted around the circumference of the wheel or drum such that each tool cuts a small portion of the hard surface, thereby advancing the cut. The tools of such machines are symmetrical around a longitudinal axis and have a hardened cutting tip and a cylindrical mounting portion rotatably retained in a tool mount on the circumference of the wheel or drum such that the tool can rotate about its longitudinal axis. Rotation of the tool within the mounting member causes the tool to wear symmetrically and thereby increasing its useable life. The concrete and asphalt which is cut by such tools, however, is so abrasive that such tools nonetheless often become so worn in a single day""s use that they must be replaced. The tools rarely survive two days of use.
To replace the tools of a cutting machine, the worn tool is removed from the tool holder after which a new tool is inserted therein. As many as six hundred replacement tools are required daily for a machine used to scarf the surface of a lane of pavement of highway. It is, therefore, desirable to maximize the useful life of such tools and to provide tools which are easily inserted into the holders thereof to reduce the down time required to replace the tools in the machine.
Existing cutting tools have a tapered forward cutting end with a tungsten carbide tip. Behind the forward cutting end is a radial flange and behind the flange is a cylindrical shank having a diameter sized to fit within the cylindrical bore of the tool holder. Between the shank and the radial flange is a frustoconical portion having a ramp angle of approximately 45xc2x0 which facilitates the alignment of the tool within the tool holder. The cylindrical shank has an enlarged diameter hub at the distal end thereof and fitted around the shank, between the hub and the frustoconical portion, is a spring loaded sleeve biased to expand radially outwardly so as to bind against the inner surface of the bore in the holder and thereby retain the tool in the holder.
In use, the tool rotates within the spring loaded retaining sleeve around the shank and the rear surface of the radial flange rotates on the forward surface of the tool holder. The rotation of the radial flange of the tool on the forward surface of the tool holder causes the forward surface thereof to become worn away and, over a period of time, an indentation or a counterbore wears in the forward surface of the tool holder, the diameter of which is substantially equal to the outer diameter of the cylindrical radial flange. Over time, the counterbore within the forward end of a tool holder can be as deep as {fraction (3/16)} of an inch.
When a replacement tool is inserted into the tool holder for which a counterbore has been worn into the forward surface thereof, the outer diameter of the radial flange of the replacement tool must rotatably fit within the inner diameter of the counterbore. If the outer diameter of the flange is equal to or larger than the inner diameter of the counterbore, it will bind against the inner surface of the counterbore and inhibit the rotation of the tool within the tool holder and thereby cause the tool to become prematurely worn. To prevent the outer circumference of such flange from locking within the counterbore in the tool block, it is desirable to provide tools for which the radial flanges thereof all have equal outer diameters. Such tools are presently cold formed using existing technology in which a metal blank is formed into the desired shape. Since the volume of the metal remains constant, cold forming require that the forming die include an opening through which excess metal can be released, and usually the portion having the largest diameter is chosen to receive the excess metal. Existing cold formed tools have an enlarge outer flange diameter which is irregular in shape because that is where excess metal is released. To insure that such radial flanges all have equal outer diameters, it is presently necessary to machine such outer diameters. The machining step, however, is expensive, and it would be desirable to manufacture tool bodies without machining the outer circumference of the flange.
The rotatability of a tool within a tool holder is also reduced by resistance between the cylindrical shank and the spring loaded retaining sleeve. Although the sleeve is designed to be retained between the forward end of the hub and the frustoconical portion of the tool, if the sleeve is not properly positioned within the tool holder the forward end of the sleeve can become wedged against the frustoconical portion of the tool. The sleeve tends to ride up the 45 degree angle of the frustoconical section thereby increasing the friction between the parts.
Friction also occurs between the outer circumference of the hub at the distal end of the shank and the inner wall of the cylindrical bore into which the shank of the tool is fitted. When the tool is used to cut a hard surface, substantial forces are applied perpendicular to the longitudinal axis of the tool, and complimentary forces are applied between the inner surface of the cylindrical bore and the outer circumference of the hub. These transverse forces increase the resistance to rotation of the tool body within the tool holder and wear away the inner surface of the tool holder.
A third source of friction which reduces the rotatability of the tool is friction against the outer wall of the shank as it rotates within the retaining sleeve. As the tool is used, fine particles of hard material work their way under the radial flange and across the forward surface of the tool holder until they fall into the bore of the holder. Some of those particles work their way down the bore of the holder and between the outer wall of the shank and the inner wall of the retaining sleeve. Particles also enter from the rear of the tool holder, between the hub and the bore of the block and work their way between the shank and the retaining sleeve. Eventually the particles between the shank and the retaining sleeve form a paste of grit which binds between the parts and prevents rotation of the tool, and causes premature tool failure.
In my co-pending application, Ser. No. 09/121,726 filed Jul. 24, 1998, I disclosed an improved tool holder which resists wear from the rotation of the tool within the holder by providing a tungsten carbide wear rings in countersinks located in the forward and rearward ends of the bore of the tool holder. As further explained in my co-pending application, the coefficient of friction between the metal of the tool body and the surfaces of the tungsten carbide wear rings is less than the coefficient of friction between a tool body and the metal surfaces of existing tools, thereby facilitating rotation of the tool within the tool holder. Nonetheless, the friction between the outer circumference of the hub at the distal end of a tool body and the accumulation of particles within the parts also inhibits the rotation of the tool.
In view of the foregoing, it is desirable to provide an improved method of manufacturing an axially symmetric tool for use in such tool holders which can be manufactured without requiring the machining of the outer diameters of the radial flange thereof and which will be less susceptible to wear caused by the transverse forces applied to the hubs at the distal end of the shank of the tool. It would also be desirable to provide an improved tool body which will maintain a retaining sleeve around the circumference of the shank thereof without permitting the forward end of the retaining sleeve to engage the frustoconical surface between the shank and the radial flange thereof. Finally, it would be desirable to provide a tool body which would reduce the amount of fine particles between the shank of the tool and the retaining band.
It is the present custom to cold form the tool bodies which are used in cutting machines for cutting hard surfaces. In this process, a coil of steel wire is cut into a blank, each of which is heated to an appropriate temperature, typically about six hundred degrees Fahrenheit, after which it is subjected to series of cold forming steps. In each of the steps of the manufacturing process, the blank is mechanically inserted into a die which defines a portion of the outer surface of the tool body after which a punch applies an impact to the blank, causing the outer surface of the blank to conform to the contour defined by the die. The blank is moved through a succession of such dies, during the course of which the first end thereof is tapered into a forward cutting end and the second end thereof is constricted into a cylindrical shank. The contouring of the first end into a tapered forward cutting end causes metal from the first end of the blank to be forced towards the center thereof. Similarly, the constriction of the second end into a cylindrical shank also forces excess metal towards the center of the blank. Existing cold forming machines form the radial flange by allowing excess metal moved during the cold forming process to accumulate in a bulge which becomes the flange. The bulge is forged into the flange, and some excess metal remains around the outer circumference of the flange after the tool is forged. It is this excess metal which is removed during the machining operation.
In accordance with the present invention, the die employed to define the rearward surface of the radial flange includes a cylindrical portion having an inner diameter equal to the desired outer diameter of the rearward {fraction (3/16)} of an inch of the flange. When the blank is fitted into the die and the punch is impacted against the blank, the cylindrical portion of the die will shape the rearward portion of the radial flange into a cylindrical portion of the desired outer diameter with a length of about {fraction (3/16)} of an inch. Excess metal or overfill is released forward of the cylindrical portion.
The die used to configure the rearward surface of the radial flange also configures a frustoconical portion between the cylindrical shank of the radial flange. In accordance another feature of the present invention, a shoulder is formed between the cylindrical shank and the frustoconical portion to thereby retain the retainer band around the smaller diameter portion of the shank and prevent the forward edge of the sleeve from engaging the ramp surface of the frustoconical portion.
The hub at the distal end of the shank of existing tools is presently cold formed by providing a die defining an enlarged diameter hub and xe2x80x9cbumpingxe2x80x9d the distal end of the shank, causing it to enlarge within the die and thereby form the hub. The xe2x80x9cbumpingxe2x80x9d technique commonly used is suitable for creating a hub having an overall length of no more than xc2xc inch and, therefore, it is customary for the hubs of such tools to have a length of only about {fraction (3/16)} inch. I have found, however, that where a tool body is made with the hub having a length longer than xc2xc inch, the side loads created by the forces at the forward end of the tool are distributed over a larger surface thereby causing a reduction in the resistance to rotation and a reduction in the wear caused to the inner surface of the cylindrical bore of the tool holders. I have found that a hub having a longer length can be cold formed by providing a suitable die for an elongated hub and providing a punch having a generally conically shaped forward end for impacting against the distal end of the shank. When the conical punch is impacted axially into the distal end of the cylindrical shank, the forward end of the die extends into the metal of the shank. As the conical punch enters the distal end of the shank, radial forces are applied to the metal of the shank surrounding the conical protrusion. These radial forces applied from within the shank cause the metal of the distal end of the shank to fill the cavity of the enlarged die thereby forming an elongated hub.